FI125519B - Expandable polymer beads and their production - Google Patents

Description

FLOATING POUOM METHODS AND MANUFACTURE THEREOF

Background of the Invention

Field of the Invention

The present invention relates to polystyrene beads. In particular, the present invention relates to coated expandable polystyrene (EPS) beads and a process for making them.

Description of the Related Art

Inflatable products have been used for some time, for example to improve the thermal insulation of buildings. Generally, these products are manufactured either by extrusion or by molding by swelling of polymer beads. Additives may be used to improve the desired properties of the products.

The use of expandable polystyrene (EPS) in such products is on the rise. EPS is a rigid and rigid foam with a closed cell structure and generally made from pre-expanded polystyrene beads. Common uses of these EPS beads include molded sheets for insulating buildings and packaging material for softening fragile objects. The latest advancements in the technology of these EPS beads are related to improving the thermal insulation of bead products.

EPS beads have also been used for antimicrobial purposes.

KR 20080081409 discloses a process for preparing an antibacterial styrofoam foam using colloidal silver and vinyl acetate resin in combination with expandable polystyrene which is not foamed prior to coating and drying.

JP 2009051895 discloses a resin comprising a foamed resin such as expanded polystyrene and an antimicrobial agent. The antimicrobial agent is obtained by graft polymerization of the antimicrobial polymer on the surface of the silica particle.

JP 1252641 discloses a sanitary foam obtained by dispersing a silver ion-containing zeolite on the surface of expanded styrene beads, pre-expanding and molding these beads.

However, prior art solutions do not disclose expandable beads made using the materials of this invention and coated with or mixed with antimicrobial agents in unexpanded form.

Summary of the Invention

It is an object of the present invention to provide an expandable polymer bead having anti-bacterial properties and a process for their preparation.

In particular, it is an object of the present invention to provide antibacterial expandable polymer beads to which one or more antibacterial agents have been added, either to the polymer matrix or as a bead coating.

These and other objects as well as their advantages over known expandable polymer beads are achieved by the present invention as described below and claimed.

The present invention relates to expandable polystyrene (EPS) beads containing one or more antimicrobial agents.

These anti-microbial expandable polystyrene (EPS) beads can be prepared by mixing the EPS beads, preferably by dry blending, with a solid antimicrobial agent containing at least one transition metal ion, wherein said antimicrobial agent is capable of adhering to the surface of the EPS beads.

More specifically, the expandable beads of the present invention are characterized in what is stated in claim 1.

Further, the process for making beads is characterized by what is stated in claim 12.

The invention provides considerable advantages. Thus, the present invention provides expandable polymer beads that can be used in the manufacture of foamed products, which, unlike known solutions, can be used in products such as food packaging, or in spaces such as buildings that require clean and non-contaminated surfaces.

Detailed Description of Preferred Embodiments

The present invention relates to antimicrobial expandable polymer (EPS) beads which comprise metal ions selected from silver and copper and combinations thereof as the main antimicrobial agents.

EPS can be either conventional EPS or refractory EPS.

The addition of the antimicrobial agent (s) can be accomplished either by coating the agent (s) as such or by applying the coating composition to the expandable beads or by directly adding the agent (s) to the polymer matrix. The beads are preferably coated by depositing metal ions on the surface of the beads. In particular, these metal salts are precipitated in the form of a metal salt of a fatty acid.

"Fatty acid" as used herein is intended to include carboxylic acids having aliphatic hydrocarbon moieties of at least 3 carbon atoms and which are either saturated or unsaturated.

The coating process may be carried out, for example, with a tapered screw mixer or rod blade mixer or any suitable mixing device for EPS.

Said fatty acids act, inter alia, as lubricant lubricants. They are generally used in small amounts, such as 0.005-10% o, preferably 0.01-0.5% o, based on the weight of the EPS beads. In particular 0.1 to 100% by weight, preferably 10 to 75% by weight, of these fatty acids consists of the silver or copper salts of said acids.

The metal ions are preferably selected from transition metals, more preferably from the group consisting of silver, copper and zinc and their alloys, preferably silver and an alloy of silver with copper or zinc. In particular, the beads contain from 0.005 to 10% o, preferably 0.01 to 0.5% o, of such metal ion or combination thereof based on the weight of the EPS beads.

According to a preferred embodiment of the invention, the beads contain mixtures of two or more metal salts of fatty acids, at least one metal salt derived from zinc cations, and at least one metal salt derived from silver or copper cations or their alloys.

According to another preferred embodiment, the beads contain 0.01-5% o silver or copper stearate or mixtures thereof, and optionally 0.1-10% o zinc stearate, typically approximately or slightly less than 0.1% o bead (including antimicrobial component) ) by weight. An additional advantage of silver stearate is that it acts as an anti-caking agent.

The beads may have a lubricated surface to allow the beads to swell without forming EPS agglomerates. This is achieved, for example, during conventional pre-expansion, which is accomplished by steaming and heating unexpanded beads.

Other additives can be added to the products either by mixing them in the polymer matrix or by adding them to the coating. Such other additives may include, for example, copolymers, antistatic agents, flame retardants, blowing agents, and thermal conductivity reducing agents such as graphite and carbon black.

According to one embodiment of the invention, one or more surface treatment agents are added to the beads, such as agents that increase the compatibility of the beads with the aforementioned salt ions, preferably prior to addition of the salts. For example, such agents can act as binders that increase the amount of ions bound to the bead surfaces, e.g. by altering the hydrophobicity of the bead surfaces. Examples of such agents are esters of glycerol and one or more fatty acids, in particular glycerol stearates, preferably selected from the group consisting of glycerol mono-, di- and tristearates, and preferably mixtures of two or three such stearates, to provide a suitably controlled hydrophobicity, which promotes the binding of the ions of the above salts.

The amounts of such surface treatment agents are generally 0.001 to 10% by weight, in particular 0.005 to 5% by weight, preferably 0.01 to 2.5% by weight, based on the weight of the bead.

Antimicrobial beads may be obtained by mixing, under substantially dry conditions, EPS beads with one or more solid antimicrobial agents comprising, as the principal antimicrobial agents, metal ions selected from the group consisting of silver and copper and combinations thereof, wherein said antimicrobial agents are capable of attachment. For EPS beads.

Preferably, said beads are obtained by heating the antimicrobial agent during mixing, which promotes its adhesion to the surface of the EPS beads.

The present invention further relates to a process for making coated anti-microbial expandable polystyrene (EPS) beads, comprising the step of mixing the EPS beads with a solid antimicrobial containing one or more metal ions selected from the group consisting of silver and copper and combinations thereof, wherein said antimicrobial agent is capable of adhering to the surface of EPS beads.

The antimicrobial agent can be heated during mixing, which promotes its adhesion to the surface of the EPS beads. The mixing is preferably carried out under non-shear conditions and most preferably under substantially dry conditions.

Said antimicrobial agent is selected, for example, from metal salts of fatty acids which are capable of lubricating the surface of the beads, said acids having a softening point below about 60 ° C.

In accordance with a particularly preferred embodiment of the invention, the coated expandable beads are prepared by contacting 1000 parts by weight of the beads with 0.1 to 10 parts by weight of an antimicrobial agent to form antimicrobial beads containing 0.0Ι to ΙΟ% of silver or copper ions. combinations thereof by weight of EPS beads.

Preferably, the beads are coated with 0.1-5% o silver or copper stearate or mixtures thereof and optionally 0.1-10% o zinc stearate.

The new anti-microbial expandable beads can be further treated in the same way as normal expandable polystyrene. The final densities of the formed products are from 5 to 150 kg / m 3, but preferably from 12 to 30 kg / m 3.

The pre-expanded beads formed in accordance with the present invention can be fused together by any suitable method, typically by casting into a mold or casting into a block. Mold molds or blocks made in this manner can also be subsequently cut to form any type of polystyrene foamed product or article, for example an insulating board. The cutting surface has been found to perform as well as other surfaces.

The following non-limiting examples are intended only to illustrate products and features of the preferred embodiments of the invention.

eXAMPLES

The examples use uncoated StyroChem K-710 grade EPS beads and various metal salts.

Example 1 In this example, uncoated StyroChem K-710 grade EPS beads were coated with 0.1% silver stearate following the procedure in Table 1.

Table 1. Coating instructions for the beads of Example 1

To produce these coated beads, uncoated EPS beads were coated with silver and zinc stearate in a laboratory scale blender. The stirring time used was 15 minutes and the final stirring temperature was 35 ° C. After coating, the material was pre-expanded with a batch pre-expander to a density of about 20 kg / m 3, kept in a silo for 24 hours and molded into 400 x 400 x 50 mm specimen slides. After one day, the specimen slides were cut into 50 x 50 x 10 small specimens mm. A batch of 10 specimens was recovered for both the original (cast surface sample, MSS) and cut surface (cut surface sample, CSS) measurements.

Analysis of silver ion dissolution

The specimens (MSS and CSS) prepared according to Example 1 were subjected to silver ion dissolution analysis. Material samples were tested for the ability of both material surfaces to release silver ions into deionized MQ water. The silver ion dissolution assay was performed using a sediment extraction method. The method is based on contacting the surfaces of specimens at specific times with a known volume of test solution to be exchanged, after which the silver content of each solution is measured to determine the amount of silver released during each cycle.

The experiments were performed by floating specimens on the surface of deionized MQ water, 30 ml volume. The sample containers containing the specimens were sealed and placed in an oven set at a constant temperature of 37 ° C. After 24 hours and 48 hours, the deionized MQ water was replaced. The removed test solution samples were stabilized with HNCrid of trace grade and stored in the refrigerator until silver analysis. Silver analysis of immersion solution samples was performed using an Inductively Coupled Plasma Mass Spectrometry (ICP-MS) spectrometer according to ISO 17294-220. The results are shown in Table 2, calculated as the cumulative concentrations of solutions and the cumulative relative amounts of total silver released from the 5x5 cm sample surfaces. The experiments were performed in duplicate on both sample material surfaces.

Table 2. Cumulative solubility of silver ions in sample solution prepared in Example 1 at concentrations of test solution (Pit. Ag) and relative total amount of silver (mtot. Ag) released from test surfaces.

* Results are presented as means of two replicates

The results show the exceptionally high silver release ability of both sample types in relation to the weight ratio of silver stearate to EPS. EPS beads have a silver stearate coating which is maintained throughout the expansion process, allowing the production of molded parts with high anti-microbial performance. The higher silver release capacity of the MSS samples is apparently due to the presence of intact surfaces of expanded silver beads coated on the cast surface samples with silver stearate. In the case of cut surfaces, the expanded beads are a portion of the surface of the sample formed from the inner matrix of the expanded beads, but still they are capable of providing a high silver release capability.

Investigation of surface antimicrobial activity

Surface antimicrobial activity against methicillin resistant Staphylococcus aureus (MRSA) was performed on cast surface specimens (MSS) following ISO 22196. A suspension of 1.96 x 10 6 cfu / ml microbes was prepared from pure culture. The suspension was pipetted (400 μΐ) and applied to test surfaces. The test surfaces containing the microbial suspension were covered with a plastic film and incubated at 36 ° C for 24 hours in a humidity chamber (relative humidity of at least 90%). After incubation, the samples were placed in sterile Stomacher bags, each containing 9.9 ml of buffer solution, and incubated for 5 minutes. The bags were further mixed on a Stomacher for one minute and the dilution slurry pipetted onto soy agar plates and incubated at 36 ° C. After 24 hours, the colonies were counted and the microbicidal activity determined according to the standard. Significant reductions of> log 4 were achieved with MRSA.

The results show an exceptionally high silver release ability and antimicrobial activity of the surface on the samples obtained, when the amount of silver stearate in the coating process was only 0.1% (w / w).

Further, the silver release capacity can be controlled by further reducing the amount of silver stearate by replacing part of the metal salt mass required for optimal process conditions with other metal salts of fatty acids such as zinc stearate. The following examples illustrate some useful mixtures of silver and zinc stearates.

Example 2

The procedure of Example 1 was repeated using the protocol in Table 3 containing a mixture of zinc stearate and silver stearate.

Table 3. Coating instructions for the beads of Example 2

Example 3

The procedure of Example 1 was repeated using the protocol in Table 4 containing a mixture of zinc stearate and silver stearate.

Table 4. Coating instructions for the beads of Example 3

Example 4

The procedure of Example 1 was repeated using the procedure in Table 5.

Table 5. Coating instructions for the beads of Example 4

Claims (20)

1. Antimicrobial expandable polystyrene (EPS) beads, comprising silver ions as major antimicrobial agents, and which are precipitated on the surface of the beads in the form of a fatty acid metal salt. An antimicrobial bead according to claim 1, wherein the silver ions are precipitated on the surface of the beads. An antimicrobial bead according to any one of the preceding claims, wherein the beads contain 0.01-10% o silver calculated on the basis of the weight of the EPS beads. An antimicrobial bead according to any one of the preceding claims, wherein the beads have a lubricated surface which allows for expansion of the beads without the formation of EPS agglomerates during conventional pre-expansion, which is carried out by evaporation and heating of the beads. The antimicrobial beads according to any one of the preceding claims, wherein the beads contain silver salts of fatty acids. The antimicrobial beads of claim 5, wherein the beads contain mixtures of one or more metal salts of fatty acids, wherein at least one metal salt is derived from zinc cations and one metal salt is derived from silver cations. An antimicrobial bead according to any one of the preceding claims, wherein the beads contain 0.1-5% o silver stearate based on weight and optionally 0.1-10% zinc stearate based on weight. Antimicrobial beads according to any one of the preceding claims, which beads can be obtained by mixing under substantially dry conditions EPS beads with one or more solid antimicrobial agents comprising silver ions as the most important antimicrobial agents, said antimicrobial agents being capable of at the surface of the EPS beads. The antimicrobial beads of claim 8, wherein said beads can be obtained by heating the antimicrobial agent during mixing, which promotes its attachment to the surface of the EPS beads. An antimicrobial bead according to claim 8 or 9, wherein said antimicrobial substance is a metal salt of a fatty acid which is cable to lubricate the surface of the beads. Antimicrobial beads according to any one of the preceding claims, further comprising one or a plurality of surface treatment agents which are preferably selected from the group comprising esters of glycerol, in particular mono-, di- or tri-esters derived from glycerol and one or more fatty acids, preferably mono-, di- and tristearates of glycerol, which are preferably a mixture of two or three of these stearates. A process for producing antimicrobial expandable polystyrene (EPS) beads, the process comprising a step of mixing EPS beads with a solid antimicrobial substance which is in the form of a fatty acid metal salt and containing metal ions selected from the group comprising silver, copper and combinations thereof, said antimicrobial being capable of being attached to the surface of the EPS beads. The method of claim 12, wherein the antimicrobial agent is heated during mixing, which promotes attachment to the surface of the EPS beads. A process according to claim 12 or 13, wherein the mixture is carried out under dry conditions or substantially dry conditions. The method of any one of claims 12-14, wherein the antimicrobial is a metal salt of a fatty acid capable of lubricating the surface of the beads, the softening point of said acid being below about 60 ° C. The method of any one of claims 12-15, wherein the mixing of EPS beads with the solid antimicrobial agent is carried out under conditions of non-cutting forces. The method of any one of claims 12-16, wherein 1000 parts by weight of beads are contacted with 0.1-10 parts by weight of antimicrobial agent, wherein antimicrobial beads are formed which contain 0.01-10% o silver or copper or combinations thereof. calculated on the basis of the weight of the EPS beads. A method according to any one of claims 12-17, wherein the beads are coated with 0.1-5% o silver or copper stearate or mixtures thereof by weight and optionally 0, Ι-ΙΟ% o zinc stearate calculated on the basis of weight. A method according to any one of claims 12-18, wherein the beads are applied to one or a plurality of surface treatment agents at the same time as the antimicrobial agents are applied or before, preferably before, and mixed under dry conditions or substantially dry conditions. An expanded polystyrene product obtained by expansion of antimicrobial expandable polystyrene beads according to any one of claims 1-11.